Hydraulic braking apparatus for motor vehicles

ABSTRACT

THE INVENTION RELATES TO AN HYDRAULIC ANTI-SKID BRAKING SYSTEM WHICH WILL OPERATE TO PRODUCE AT LEAST PARTIAL BRAKING, THAT IS BRAKING OF AT LEAST SOME OF THE WHEELS OF A VEHICLE, EVEN IN THE EVENT OF FAILURE OF PART OF THE SYSTEM CAUSING A LOSS OF PRESSURE IN THAT PART. THE BRAKING SYSTEM IS NORMALLY SERVO ASSISTED BUT IS ARRANGED TO PRODUCE BRAKING WITHOUT SERVO ASSISTANCE IN THE EVENT OF A FAILURE OF THE ENGINE OF THE VEHICLE OR THE PUMP WHICH PRODUCES THE SERVO ASSISTANCE. THE BRAKING CIRCUIT IS FORMED IN TWO INDEPENDENT PARTS EACH OF WHICH COMPRISES A LOOP AROUND WHICH FLUID IS CONTINUOUSLY CIRCULATED BY A PUMP DRIVEN BY THE ENGINE, THE PRESSURE OF FLUID IN THE LOOP IS CONTROLLED BY A MODULATOR VALVE WHICH IS CLOSED WHEN THE BRAKES ARE OPERATED, TO INCREASE THE PRESSURE AND OPERATE BRAKING ACTUATORS WHICH ARE EITHER IN SERIES IN THE LOOP OR IN STATIC BRANCHES OF THE CIRCUIT COMMUNICATING WITH THE LOOP. A PRESSURE SENSITIVE VALVE IS PROVIDED TO ENSURE THAT FLUID ALWAYS FLOWS IN THE CORRECT DIRECTION AROUND THE LOOP EVEN IN THE VENT OF A FAILURE CAUSING AN ADVERSE PRESSURE DIFFERENTIAL.

United States Patent 91 Peruglia et al.

[54] FAILSAFE HYDRAULIC BRAKING APPARATUS FOR MOTOR VEHICLES [75]Inventors: Marco Peruglia, Turin; Giancarlo Michellone, Cambiano, bothof Italy [73] Assignee: Fiat Societa per Azioni, Turin, Italy [56]References Cited UNITED STATES PATENTS 3,545 8l4 [0/1970 Marcetts..303/6 C 3,637,963 l/l972 Wellman ....303/6 C X 3,674,954 7/1972 Kish &Swanson ..303/6 C X Primary ExaminerAllen N. Knowles AssistantExaminerGene A. Church Attorney-Richard C. Sughrue et al 1 Apr. 17, 1973[57] ABSTRACT The invention relates to an hydraulic anti-skid brakingsystem which will operate to produce at least partial braking, that isbraking of at least some of the wheels of a vehicle. even in the eventof failure of part of the system causing a loss of pressure in thatpart. The braking system is normally servo assisted but is arranged toproduce braking without servo assistance in the event of a failure ofthe engine of the vehicle or the pump which produces the servoassistance. The braking circuit is formed in two independent parts eachof which comprises a loop around which fluid is continuously circulatedby a pump. driven by the engine, the pressure of fluid in the loop iscontrolled by a modulator valve which is closed when the brakes areoperated, to increase the pressure and operate braking actuators whichare either in series in the loop or in static branches of the circuitcommunicating with the loop. A pressure sensitive valve is provided toensure that fluid always flows in the correct direction around the loopeven in the vent of a failure causing an adverse pressure differential.

PATENTED APR I 71975 SHEET 1 [IF 6 IIIII I'll..-

PATENTEB APR 1 7 I975 SHEET 2 [IF 6 PATENTED APR) 71975 SHEET 3 OF 6 8388 &2% or PATENTE APR 1 7 I973 SHEET 5 BF 6 nmm :1 In-m E ommPATENTEUAPR 1 7197s SHEET 8 BF 6 FAILSAFE HYDRAULIC BRAKING APPARATUSFOR MOTOR VEHICLES BACKGROUND OF THE INVENTION The present inventionrelates to hydraulic braking systems for motor vehicles, andparticularly to improved hydraulic braking systems having a number ofsafety features. One feature of braking systems of this invention isthat they can continue to operate to provide some degree of braking evenin the event of failure of a part of the circuit.

Another feature of some embodiments of the invention is that cooling ofthe braking actuators can be effected using the same hydraulic fluidwhich operates the actuators, without requiring any separate coolingfluid for the braking actuators and without requiring special provisionfor air circulation around the actuators.

SUMMARY OF THE INVENTION According to the present invention, there isprovided an hydraulic braking system for a pair of wheels of a motorvehicle, comprising an hydraulic circuit including a pump operable tocirculate hydraulic brake fluid around a part of the circuit formed as aloop which includes a modulator valve operable by a brake pedal torestrict the flow of fluid around the said loop to increase the pressurein the fluid between the pump and the modulator valve so as to operatebraking actuators of the said pair of wheels, which are connected insaid circuit, characterized in that in the event of failure of the pump,the modulator valve is operable, when the brake pedal is depressed topressurize the fluid in the part of the circuit containing the brakeactuators and in that the circuit includes a first retainer valvebetween the said pump and the said modulator val-ve which allows fluidflow in a direction from the pump to the modulator valve but whichprevents fluid flow in the opposite direction.

Various other features and advantages of the invention will becomeapparent during the course of the following description of severalpreferred embodiments of the invention which is given purely by way ofnonrestrictive example.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic circuit diagramof a part of a braking system in which the circuit for the front wheelsis entirely separated from the circuit for the rear wheels, only thecircuit for the front wheels being shown in the drawing;

FIG. 2 is a circuit diagram of a modified form of the front circuit ofthe braking system of FIG. I, in which the brake actuators are cooled;

FIG. 3 illustrates a second embodiment of the invention which is abraking system including two pumps but having only one modulator of aform which will be referred to hereinafter as a duplex" modulator, thatis one having two separate operating chambers for two separated partsofa circuit;

FIG. 4 shows a modified form of the braking system of FIG. 3, in whichthe brake actuators are cooled;

FIG. 5 illustrates a third embodiment of the invention which has twopumps and a duplex" modulator; and

FIG. 6 illustrates a modified form of the braking system of FIG. 5, inwhich the brake actuators are cooled.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 thereis shown part of a hydraulic braking circuit, the parts shown being forbraking a pair of wheels, which may be either the front or rear wheelsof a motor vehicle. In practice a motor vehicle would be fitted with twoidentical braking circuits as shown in FIG. 1, but controlled by asingle control member which will be described below.

In the circuit of FIG. 1 a volumetric pump 10 driven by the engine (notshown) of the vehicle draws hydraulic fluid from a reservoir 12, througha pipe 14 and pumps it through a pipe 16 to a pressure switch 18 whichis operative in the event of failure of the pump or the engine drivingit, or in the event of a rupture in the pipe from the reservoir leadingto a fall in pressure, stops the action of an anti-skid device (notshown) which does not form part of the invention and hence is neitherillustrated nor described. From the pressure switch 18 a pipe 20 leadsto a retainer valve 22, and from there a pipe 24 is connected to theinlet of a modulator valve 26 the outlet of which is connected through apipe 28 to the hydraulic fluid reservoir 12.

The modulator valve 26 comprises a cylinder 30 within which there isslidable a piston 36 which has an axial passageway 38. The piston 36separates the cylinder 30 into two chambers 32 and 34. A return spring40 normally urges the piston 36 to the left in the orientation shown inFIG. 1. A plunger 42 having a tapered or conical end face is guided in ahole in the end wall of the cylinder 30 and biased to the left, in theorientation shown in FIG. 1, by a spring 44 which is considerably weakerthan the spring 40. When the plunger 42 is moved against the action ofthe spring 44 it progressively closes the holes 38 in the piston 36 withits tapered or conical end.

The outlet of the retainer valve 22 is also connected via a pipe 46 andtwo branch pipes 48 and 50 to respective anti-skid distributor valves52, 54 which normally establish communication between the pipe 46 andrespective brake actuators 62 and 64 but which can be controlled todischarge the hydraulic fluid from the brake actuators 62, 64 to thereservoir 12 by an antiskid control device (not shown), which does notform part of the invention and which will therefore not be described indetail.

The plunger 42 is linked to the brake pedal by means of a rocker (notshown) to which is also connected a corresponding plunger ofa brakingcircuit for the other two wheels of the vehicle. Adjustment of the pinof the rocker is effected una tantum to adjust the ratio between thefront and rear braking pressures to suit the individual conditions suchas where special roads are travelled, or to suit the conditions in thecase of motor racing.

Under normal conditions when the vehicle is operating hydraulic fluid isdelivered from the volumetric pump 10 through the pipe 16, the pressureswitch 18, the pipe 20, the retainer valve 22, and the pipe 24, itpasses freely through the modulator valve 26 from the inlet port 27 tothe outlet port 29, and returns to the reservoir 12, through the pipe28. Hence there is no appreciable pressure in the pipe 46 so thatneither of the brake actuators 62, 64 are operated.

When the brake pedal is operated the plunger 42 is moved against theresistance of the spring 44 and the passageway 38 in the piston 36 isprogressively restricted giving rise to an increase of pressure upstreamof the modulator valve 26 in the loop circuit just described. Thepressure in the pipe 46 and in the branches 48 and 50 thus rises and thebrake actuators 62, 64 are operated. It will be appreciated that theforce required on the plunger 42 to effect braking is rather less thanthe force required to create a given braking pressure in the actuatorsso that the system provides servo assistance under normal conditions.

If the engine stops or in the event of failure of the volumetric pump sothat the circulating flow of fluid ceases, the plunger 42 presses thepiston 36 against the resistance of the spring 40, completely closingthe passageway 38 of the piston 36 so that the piston 36 acts to pumpfluid from the port 27 into the pipe 24. The retainer valve 22 preventsthis fluid from flowing towards the volumetric pump 10 and thence to thereservoir through the pipe 14. Instead, the fluid flows into the pipe 46and from there into the branches 48 and 50 so as to exert a pressure onthe brake actuators 62, 64 to operate them. In this emergency braking"mode of operation the force required on the plunger to move the pistonis that required to create the braking pressure in the circuit so thatit will be seen that the system operates without servo-assistance inthis mode.

In the event of total failure of one of the two braking circuits of themotor vehicle, then since they are entirely independent the other isalways available to produce braking of at least two of the wheels of thevehicle. The anti-skid device will continue to operate normally in onepart of the circuit, in the event of failure of the other part of thecircuit .but will be switched off automatically in either circuit in theevent ofa failure in the loop'part of the circuit, that is incircumstances such as when the modulator valve 26 operates as a pump.

In FIG. 2 there is shown a system similar to the system illustrated inFIG. I but modified in order to provide cooling of the brake actuators.

Corresponding components in all of the drawings are referred to by thesame reference numerals as those used in FIG. 1 but with a prefixrepresenting the figure before each and a suffix a or p representing thecorresponding component ofa front or rear braking circuit respectively,where both circuits are illustrated.

In FIG. 2 hydraulic fluid is delivered from a pump 210 but instead ofgoing directly to a modulator valve 226 it is passed first through apipe 246 to the braking actuators 262, 264 via respective hydraulicdistributor valves 252, 254. The actuators 262, 264 of this embodimentare fitted with inlet and outlet ports 261, 263 and 265, 267respectively so that hydraulic fluid can flow through them, theactuators being operated when the pressure of the hydraulic fluidincreases regardless of its flow, that is whether there is any flow ornot. The outlet ports 265, 267 are connected through respective pipes266, 268 and respective retainer valves 270, 272 to a pipe 274 whichleads to the inlet port 227 of the modulator valve 226. The inlet port227 of the modulator valve 226 is also connected to the pipe 246 betweenthe retainer valve 222 and the hydraulic distributors 252 and 254 by apipe including a further retainer valve 276 which allows fluid flow in adirection from the inlet port 227 to the pipe 246 but which preventsfluid flow in the opposite direction. In normal operation this valve isshut since there is a slight pressure difference across it when fluid iscirculating through the loop which is completed by a pipe 228 connectingthe modulator valve 226 to the reservoir 212, and which in this case isconstructed with a plurality of cooling fins 213, so that it can act asa heat exchanger between the hydraulic fluid and the surroundings. Inthis case the fluid circulates through the brake actuators 262, 264 whenthe pump 210 is working (and providing the plunger 242 is not entirelyclosing the opening 238), thereby removing their heat, which is thengiven up by the reservoir 212 to the surroundings.

As with the embodiment of FIG. 1 operation of the modulator valve 226reduces the flow through the pipe 274 to the reservoir 212, thusincreasing the pressure in the loop circuit and therefore in the brakecylinders 262, 264.

If the engine stops or the pump 210 fails then, as in the embodiment ofFIG. 1, the piston 242 is moved by the plunger to increase the brakingpressure without servo-assistance; again the anti-skid control device(not shown) is switched off by the pressure switch 218. In this eventthe valve 276 operates to allow fluid to flow to the pipe 246 and thenceto the brake actuators 262, 264, since the retainer valves 270 and 272prevent fluid flow in the opposite direction from the normal circulationin the loop. These valves 270 and 27 2 are necessary, however, to ensureproper anti-skid operation under normal circumstances.

During normal braking the flow of fluid through the reservoir 212 variesin inverse proportion to the braki'ng pressure, and returns to itsoriginal value as soon as the brake pedal is released, or whenever theanti-skid device operates to release the braking pressure when skiddingis imminent. This should normally be sufficient to cope with the risk ofboiling, brought about by any drop in pressure with increase oftemperature in the brake actuators.

It is possible to introduce into the tank 212 a thermometer (notillustrated) which will indicate to the driver of the motor vehicle thetemperature of the hydraulic braking fluid, and consequently thetemperature of the front and rear brake actuators. Again the presence oftwo entirely independent circuits ensures that at least some brakingaction is available, even in the event of total failure of one of thecircuits.

In FIG. 3 there is shown a circuit diagram of a second embodiment of theinvention illustrating a complete braking system for the front and rearwheels of a motor vehicle.

This second embodiment also comprises two circuits having separate pumpsand reservoirs for the front and the rear wheels. In this embodimenthowever, the two circuits are not entirely independent as are the twocircuits of the preceding embodiment since the two modulator valves arereplaced in this latter embodiment by a single modulator valve of theduplex type which will be described below.

The duplex modulator is formed in two parts 326a, and 326p which areseparated by a baffle 378 which has an opening which guides a plunger342a of the part 326a which is otherwise identical to the modulatorvalve 26 of the preceding embodiment. The part 326a has an inlet port3270, an outlet port 329a, springs 340a, 344a, and a piston 336a. Theplunger 342a is operated by the fluid pressure in the other part 326b ofthe modulator valve 326.

The rear part 326p of the modulator valve 326 is constructed identicallywith the front part 326a, and hence with the modulator 26 of FIG. 1,except that the plunger 342p is operated directly by the brake pedal(not illustrated) without the interposition of a rocker as in thepreceding embodiment since only the one plunger is connected thereto theother plunger 3420 being operated, as mentioned above, by the pressurein the chamber 332p caused by the operation of the plunger 342p.

The remainder of the circuit is the same as two circuits of the typedescribed in relation to FIG. 1.

Each of the two parts of the system, however, has the samecharacteristics of safety and protection from pump breakages, etc., asthe embodiment of FIG. 1. In particular, in the event ofa total loss offluid pressure in the circuit containing the rear chamber 332p of themodulator valve the plunger 342p, when moved by the brake pedal (notshown) pushes the piston 336p to the right, in the orientation shown inFIG. 3, until it engages the end of the plunger 342a to operate it.

In FIG. 4 there is shown a modified embodiment which is like the brakingsystem of FIG. 3, but which also operates to cool the brake actuators.The differences between this circuit and the circuit of FIG. 3 are thatthe braking actuators 462a, 464a, 462p and 464p are connected into theloop circuit, to receive a throughflow of circulating fluid in a mannersimilar to the embodiment of FIG. 2.

It is not therefore necessary further to describe either theconstruction or the operation of this embodiment since these followdirectly from the description of the systems illustrated in FIGS. 2 and3 respectively.

In FIG. 5 there is shown a third embodiment of a braking systemaccording to the invention.

This embodiment is a simplified version of the embodiment illustrated inFIG. 3, and differs from it in that the duplex modulator valve 526 issimplified. The modulator valve 526 includes a chamber 526a having nopiston so that it does not operate to increase the pressure in thecircuit of the front brakes in the emergency braking" situation withoutservo-assistance in the event of failure of the pump. Emergency brakingis thus available only to the rear brake circuit. This embodiment ischeaper to manufacture by virtue of the fact that a retainer valve inthe front circuit is not required, as can be seen from FIG. 5.

FIG. 6 illustrates a modified circuit similar to the circuit of FIG. 5,in which the brake actuators are cooled by the brake fluid in a mannersimilar to that of the embodiments of FIGS. 2 and 4, by including thebrake actuators in branches of the loop circuit around which thehydraulic fluid is circulated. Again, the operation of this embodimentfollows from the description of the preceding embodiments and so willnot be described again as this would be merely repetitious.

Naturally, many modifications and alterations can be made to theembodiments of the invention described by way of example withoutdeparting from the spirit and scope of the invention.

We claim:

1. In a hydraulic braking system for two of the wheels of an automobile,of the type in which part of the circuit is formed as a loop including:

reservoir means,

pump means circulating hydraulic fluid from said reservoir means aroundsaid loop and back to said reservoir means;

modulator valve means;

brake pedal means, means operatively connecting said brake pedal meansto said modulator valve means;

brake actuator means, means connecting said brake actuator means to saidcircuit between said pump means and said modulator valve means, saidmodulator valve means operating, when controlled by said brake pedalmeans, to restrict the flow of fluid around said circuit to increase thepressure in said hydraulic fluid between itself and said pump means suchas to operate said brake actuator means, the improvement comprising:

first one way valve means in said circuit between said pump means andsaid modulator valve means, said first one way valve means operating toallow fluid to flow through it from said pump means to said modulatorvalve means and to prevent fluid from flowing through it from saidmodulator valve means to said pump means,

said modulator valve means being operable to pressurize the fluid in thepart of said circuit containing said brake actuator means in the eventof a failure of said pump means.

2. The braking system of claim 1 wherein said brake actuator means arelocated in a branch of said circuit connected to said loop part of saidcircuit at a junction located between said pump means and said modulatorvalve means, said first one way valve means being connected in said looppart of said circuit between said junction and said pump means.

3. The braking system of claim I further comprising:

inlet and outlet ports on said braking actuator means,

said braking actuator means being connected in parallel in respectivebranches of said loop part of said circuit, respective second one wayvalve means in respective said branches of said loop part of saidcircuit between said brake actuator means and said modulator valvemeans, said second one way valve means allowing fluid flow in adirection from said brake actuator means to said modulator valve meansand preventing fluid flow in the opposite direction,

third one way valve means connecting said modulator valve means to saidloop circuit between said first one-way valve means and said brakeactuator means, said third one way valve means allowing fluid flowthrough itself from said modulator valve means to said loop circuit andpreventing fluid flow through itself from said loop circuit to saidmodulator valve means.

4. The hydraulic braking system of claim 1 wherein said reservoir meansof said circuit is provided with heat exchanger means for exchangingheat from said braking fluid therein to the surroundings thereof.

An hydraulic braking circuit for two pairs of wheels of an automobilecomprising respective said hydraulic braking systems of claim 1 for eachpair of wheels wherein there are means connecting said modulator valvemeans of each system to said brake pedal means whereby operation of saidbrake pedal means causes said two modulator valve means to operatesimultaneously.

6. An hydraulic braking circuit for two pairs of

2. The braking system of claim 1 wherein said brake actuator means arelocated in a branch of said circuit connected to said loop part of saidcircuit at a junction located between said pump means and said modulatorvalve means, said first one way valve means beIng connected in said looppart of said circuit between said junction and said pump means.
 3. Thebraking system of claim 1 further comprising: inlet and outlet ports onsaid braking actuator means, said braking actuator means being connectedin parallel in respective branches of said loop part of said circuit,respective second one way valve means in respective said branches ofsaid loop part of said circuit between said brake actuator means andsaid modulator valve means, said second one way valve means allowingfluid flow in a direction from said brake actuator means to saidmodulator valve means and preventing fluid flow in the oppositedirection, third one way valve means connecting said modulator valvemeans to said loop circuit between said first one-way valve means andsaid brake actuator means, said third one way valve means allowing fluidflow through itself from said modulator valve means to said loop circuitand preventing fluid flow through itself from said loop circuit to saidmodulator valve means.
 4. The hydraulic braking system of claim 1wherein said reservoir means of said circuit is provided with heatexchanger means for exchanging heat from said braking fluid therein tothe surroundings thereof.
 5. An hydraulic braking circuit for two pairsof wheels of an automobile comprising respective said hydraulic brakingsystems of claim 1 for each pair of wheels wherein there are meansconnecting said modulator valve means of each system to said brake pedalmeans whereby operation of said brake pedal means causes said twomodulator valve means to operate simultaneously.
 6. An hydraulic brakingcircuit for two pairs of wheels of an automobile comprising respectivesaid hydraulic braking systems of claim 1 for each pair wherein thereare means connecting said modulator valve means of said two systemstogether and, means connecting one said modulator valve means to saidbrake pedal means, said other modulator valve means being operated bythe pressure in said one modulator valve means.